# 钟奕升
# 调用函数求2+4+...+n,当输入n为奇数时，调用函数1+3+...+n
def func():
    k = int(input("输入一个数"))
    num = 0
    if(k % 2 == 0):
        for i in range (2,k+2,2):
            num += i
    else:
        for i in range (1,k+2,2):
            num += i
    print(num)
while 1:
    func()